High-dose administration of methamphetamine (METH) causes persistent striatal dopaminergic deficits. In addition, our laboratory was the first to demonstrate that METH treatment causes formation of high molecular weight dopamine (DA) transporter (DAT)-associated complexes in vivo. This proposal tests the hypothesis that this complex formation is associated with, and may contribute to, the dopaminergic deficits caused by the stimulant. This will be tested by accomplishing the following Specific Aims: A. Identifying the significant features of METH-associated DAT complex formation. In particular, we will examine: 1) the dose- and time-response effects of METH treatment on DAT complex formation;2) the regional selectivity of METH-induced DAT complex formation;3) if transporter complex formation is unique to DA neurons;4) the species specificity of METH-induced DAT complex formation;5) if DAT complex formation is a unique consequence of METH treatment;and 6) the identity of the DAT complexes. B. Elucidating mechanisms underlying METH-induced DAT complex formation. In particular, we will investigate the roles of reactive oxygen species, reactive nitrogen species, aberrant VMAT-2 function and newly synthesized DAT to complex formation. C. Investigating consequences of DAT complex formation. A few investigators have demonstrated transporter complex in vitro, and have hypothesized that this may alter transporter expression at the plasmalemmal membrane. Beyond this, little is known regarding the potential consequences of DAT complex formation. We will address this issue by examining if the formation of DAT complexes: 1) influences transporter trafficking;2) alters DA uptake/release;and 3) is necessarily linked to toxicity. In summary, preliminary data presented herein are the first to demonstrate that METH causes high molecular weight DAT-associated complex formation in vivo. Completion of the Aims described above will not only contribute to our understanding of the effects of METH on DA neurons, but also the physiological regulation of DAT. This, in turn, may enhance understanding of a variety of DAT-associated disorders ranging from stimulant abuse to neurodegenerative diseases such as Parkinson's disease.